A liquid crystal display usually uses progressive scanning to drive a liquid crystal display screen. FIG. 1 is a schematic diagram for pixel electrode driving of a thin film transistor liquid crystal display screen. As shown in FIG. 1, each pixel on a liquid crystal display can be equivalent to a liquid crystal capacitor (CLC) and a storage capacitor (Cstg), one terminal of a pixel electrode is connected to a drain of a thin film transistor (TFT), a source of the TFT is connected to data lines (Sn, Sn+1) of the display screen, a gate of the TFT is connected to gate lines (Gn, Gn+1) of the display, and the other terminal of the pixel electrode is connected to a common electrode (Vcom) of the liquid crystal display screen.
Currently, a driving method of a pixel electrode of a liquid crystal display device is to charge the pixel electrode, and the charge amount being charged on each pixel electrode depends on respective gray scale of each pixel; and a common electrode uses a constant voltage driving method, that is, a common electrode voltage is a fixed voltage value regardless what graphical image the liquid crystal display outputs, and what charge amount is on a pixel electrode. FIG. 2 is a structure diagram of the driving device of a common electrode of prior art. As shown by FIG. 2, the common electrode driving circuit comprises resistors R1 and R2 and an adjustable resistor R3. A high voltage provided by power supply (AVDD) is divided by R1, R2 and R3, and then processed by an operational amplifier to obtain a common electrode voltage Vcom, and the common electrode voltage drives the common electrode of liquid crystal display.
For the prior art using a fixed common electrode voltage to drive a liquid crystal display, there are problems as follow: when a pixel electrode is driven by a driving circuit, it is impossible to keep total charge amount of positive charges and negative charges on the pixel electrode as zero, and there may be more positive charges or negative charges on the pixel electrode for some specific graphical images. Since the charge amount on the common electrode is equal to that on the pixel electrode, a larger common electrode current is needed to make compensation when the charge amount on the pixel electrode has severe unbalanced situation, however, since common electrode wires in the common electrode driving circuit have some impedance which delays the common electrode voltage's arrival at the pixel electrode, the voltage on the pixel electrode is not the target voltage at this moment, thus image quality displayed during this stage is deteriorated dramatically.